Solid fuel boiler

ABSTRACT

The present invention relates to a solid fuel boiler, comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage, and an outlet for hot air, wherein the flue gas passage comprises a tube kit with a plurality of tubes arranged adjacent to each other to create a flow space for air between the tubes, wherein at least one of said tubes is arranged so that it extends obliquely upwards in an acute angle in relation to the vertical line of the boiler from a lower attachment point to an upper attachment point.

This application claims priority to U.S. Provisional App'n Ser. No. 61/095,327, filed 9 Sep. 2008, the complete disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a solid fuel boiler, comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage and a hot air outlet, wherein the flue gas passage comprises a tube kit with a plurality of tubes adjacent to each other which are arranged to create a flow space for air between the tubes.

PRIOR ART

The present invention relates to a biofuel boiler for solid fuel for central heating of buildings, e.g. with pellets or corn, of the type where the heat from the combustion gases is converted to heating air via a heat exchanger comprising a plurality of usually parallel tubes.

Many different types of such a biofuel boiler are known. Through e.g. U.S. Pat. No. 5,123,360, U.S. Pat. No. 5,243,963, U.S. Pat. No. 5,331,943 and U.S. Pat. No. 5,873,356 different types of such solid fuel boilers are known which all have the common characteristic that the heat exchanger has tubes horizontally arranged. A great drawback with this type of boiler is that the horizontally arranged tubes imply that the boiler will become very wide. Thus, such a construction is often not desirable from considerations of space.

Through U.S. Pat. No. 4,217,878 and U.S. Pat. No. 4,579,102 it is shown that also the opposite principle is known, i.e. a heat exchanger with vertical tubes, which in certain connections is more favourable as to space.

A common problem, no matter which of the two principles mentioned above is used, is that it is difficult to combine good utilization of the existing spaces in buildings and at the same time to be able to obtain the desired output power, above all in a combination that it will be possible to manufacture the boiler in a cost efficient manner. Existing boilers therefore often involve that an expensive adaption of either the boiler or the building must be performed and/or that a non-optimal utilization of the space of the building must be accepted. An additional common problem is that they often have a comparatively low efficiency.

DISCLOSURE OF THE INVENTION

An object of the present invention is to eliminate or at least minimize the problems mentioned above, which is obtained by means of a solid fuel boiler comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage and a hot air outlet, wherein the flue gas passage comprises a tube kit with a plurality of tubes adjacent to each other which are arranged to create a flow space for air between the tubes, wherein at least one of said tubes is arranged so that it extends obliquely upwards in an angle in relation to the vertical line L of the boiler from a lower attachment point to an upper attachment point.

Thanks to the invention, a solid fuel boiler for heat exchange between the combustion gases and air is provided, which results in high efficiency and hence a high output power at the same time as a limited space is needed for the location of the boiler. The reason is simply that the convection surfaces and the flow paths which are obtained by means of a construction according to the invention in an effective way, both from an energy and cost point of view, makes it possible to achieve a large heat transfer within a limited space; in other words, the creation of a compact and high efficient solid fuel boiler.

According to the preferred aspects of the invention:

said tubes are parallelly arranged and are preferably straight, which enables a specially cost efficient and rational manufacture;

said tubes are arranged in several rows in a displaced manner, whereby the hot air as to its main flow direction is forced to turn to and fro through the tube kit, which results in especially good heat exchange;

the fire space is arranged at the bottom with a centre displaced towards a first side wall of the boiler, and the flue gas outlet is arranged at the top, near, or inside, in a, in relation to said first side wall, opposite second side wall of the boiler, which improves the efficiency further;

the convection space is provided with at least one partition wall, arranged to force the air flow essentially across the tube kit, and the air flow is preferably forced to cross the tube kit at least twice, which improves the efficiency further;

the air flow before its exit through the outlet passes at least one passage which has at least one wall, the opposite side of which is a delimitation of the fire place, which also are properties which increases the efficiency further;

the outlet for hot air is arranged in the lower half of the boiler and adjacent to said fire place, which implies the possibility to compactness;

the boiler is provided with an essentially parallel-epipedic housing, the height h of which essentially exceeds the width b and the depth d, and preferably h>d>b, which implies an extremely good possibility to effective utilization of large spaces in a building.

BRIEF DESCRIPTION OF DRAWINGS

Below the invention will be described more in detail with reference to the enclosed drawings, of which:

FIG. 1 schematically shows the principle construction of a solid fuel boiler according to the invention, seen from one side;

FIG. 2 shows an embodiment of a solid fuel boiler according to the invention in cross-section, seen from one side;

FIG. 3 shows the same boiler as in FIG. 2 in a section along the line III-III of FIG. 2;

FIG. 4 shows the same boiler in a section along the line IV-IV of FIG. 2;

FIG. 5 shows a first alternative embodiment in a section along the line IV-IV of FIG. 2;

FIG. 6 shows a second alternative embodiment in a section along the line IV-IV of FIG. 2;

FIG. 7 shows a graph of a test performed with a boiler according to the invention.

DETAILED DESCRIPTION

In FIG. 1, the principle of a solid fuel boiler according to a preferred embodiment of the invention is shown seen from the side. An essentially parallel-epipedic boiler housing 9 is shown having a height h which is about 2 to 4 time larger than the width b and with a depth d which is between 1.5 to 3 times larger than the width b. Inside the boiler 9, near its lower left corner (seen in the figure) there is a fire place 1, adjacent to which a burner 3 is connected in order to produce a flame 2 for the combustion of supplied fuel p inside the fire place 1. The flue gases g being produced in the fire place 1 pass up through the fire place 1, further through a tube kit 4, which in relation to the vertical line is positioned at an angle α, and then exit through exhaust tube 5 being located adjacent to the upper right corner of the boiler 9.

In the upper end 9E of the housing 9 of the boiler an inlet 6 and a fan 60 are arranged for intensified feeding of cold air to a convection space 7. Inside the convection space 7 a partition wall 70 is provided, extending across the tube kit 4, which forces the air flow a to cross the tube kit 4, above the partition wall 70. The outlet 71 from the convection space 7 is arranged in connection to the left wall 9A of the boiler housing 9. Thanks to the location of the opening 71 (to the left in the figure), the air flow a is, after its first passage across the tube kit 4, forced again to pass across the tube kit 4 in order via the outlet 71 to flow further through channels 12 extending in connection to the upper part of the fire place 1. In the channels (one on each side of the top of the fire place) the air flow a is fed from the left, in the figure, obliquely downwards to the right towards the outlet 8, which is located at the bottom near the right corner of the housing, i.e. at the opposite side 9C in relation to the fire place 1. Below the fire place 1, in the lower space 14 of the boiler, a movable ash pan 15 is arranged for the collection/emptying of ash 16.

Two tests performed with the boiler have shown very good results. The same burner was used at the tests (EcoTec™) but with different combustion cups, 20 kW and 25 kW, respectively, rated output.

At a first test, the burner was used with a combustion cup with a rated output of 20 kW, wherein the following values were obtained:

Fuel: Woodpellets 8.0 mm i. Heat effect 4.65 kWh/kg ii. Quantity used 23.3 kg iii. Total energy supplied 112.4 kWh iv. Total energy produced 107.0 kWh Capacity: Power (max) 18.5 kW i. Energy produced 107.0 kWh ii. Boiler efficiency 0.0% iii. Combustion efficiency 95.3% iv. Flue gas temperature (average) 141° C. v. OGC at 10% O₂ 5 mg/nm³ vi. THC (max) 4 ppm vii. THC (min) 1 ppm viii. CO at 10% O₂ 225 mg/nm³ ix. CO (max) 247 ppm x. CO (min) 130 ppm xi. NO at 10% O₂ 105 mg/nm³ xii. O₂-content 9.6%

At a second test, the burner was used with a combustion cup with a rated output of 25 kW, wherein the following values were obtained:

Fuel: Wood pellets 8.0 mm i. Heat effect 4.83 kWh/kg ii. Quantity used 25.9 kg iii. Total energy supplied 126.2 kWh iv. Total energy produced 120.5 kWh Capacity: Power (max) 23.2 kW i. Energy produced 120.5 kWh ii. Boiler efficiency 0.0% iii. Combustion efficiency 96.2% iv. Flue gas temperature (average) 140° C. v. OGC at 10% O₂ 1 mg/nm³ vi. THC (max) 2 ppm vii. THC (min) 1 ppm viii. CO at 10% O₂ 59 mg/nm³ ix. CO (max) 87 ppm x. CO (min) 39 ppm xi. NO at 10% O₂ 103 mg/nm³ xii. O₂-content 7.6%

The following can therefore be established (see also the graph, FIG. 8).

The combination results in just over 95% of combustion efficiency, which with hot air (at least in most cases) may be considered equal to utilized boiler efficiency, and must then be regarded as surprisingly good results. The combination manages by a comfortable margin the limit values which exist for emissions according to BBR (BBR=Boverket's Building Regulations; Boverket=The Swedish Board of Housing). Many emissions are at levels constituting fractions of valid environmental requirements, such as e.g. OGC=2-5 mg/nm³ at 10% O₂ (limit for approval=100 mg/nm³ at 10% O₂) and CO=39-247 mg/nm³ at 10% O₂ (limit=3.000 mg/nm³), respectively.

The tests have also proved the advantages that the boiler manages full load firing without the flue gas temperature exceeding 250° C. and that hot air temperatures as well as surface temperatures manage the safety reguirements of BBR.

An interesting result also is that the environmental values for both the tested models of pellet burners show better values than those normally obtained at operation of a boiler with a water jacket. The only reasonable explanation of this phenomenon which we are able to find is that the surrounding fire place acts less cooling on the flame and that a more stable operation with quicker starts is obtained.

In FIG. 2 a possible embodiment of a solid fuel boiler according to the invention is shown in cross-section seen from one side and in FIG. 3 it is shown in a section along the line III-III in FIG. 2. The principles of the construction are the same as described in connection with FIG. 1, and therefore only certain aspects will be described more in detail below.

The tube kit 4 consists of a plurality (normally 8 to 20, here 14) parallel tubes 40 extending in an oblique angle α in relation to the vertical line L. Thus, the tube 40 located utmost to the left (seen in the figure) extends from a position with its inlet opening 40A comparatively close to the left side surface 9A of the boiler 9, from its lower attachment point, which consists of a plate 10 in the upper part of the fire place, to a position with its upper outlet opening 40B having its attachment point in a plate 50 constituting part of the outlet 5, in such a manner that the outlet opening is closer to the right wall 9C of the boiler 9.

The tubes 40 are arranged at a distance from each other, so that a gap S is formed therebetween, which gap S suitably is about 0.1 to 0.5× the diameter D of the tube, (see FIG. 4). The tubes are arranged in several rows 40′, 40″, 40″′, 40″″ (normally 3 to 5 rows, here 4), wherein the tubes in the respective adjacent row are displaced in relation to each other in such a way that the centre line 40* for tubes in every second row 40′, 40″′ are essentially aligned seen in the main flow direction a of the hot air, while the centre line 40** for tubes in an intermediate row 40″ are essentially aligned as to the centre of the gap S seen in said flow direction a. Hence, the tubes 40 may be arranged in a compact manner in the tube kit at the same time as flow paths through the kit 4 are formed, which forces the air to turn to and fro between the tubes across the main flow direction a of the hot air. According to the preferred embodiment, both the lower ends 40A and the upper ends 40B, respectively, of the tubes are arranged at a plane plate portion 10A and 50A, respectively.

In the upper end 9E of the housing 9 of the boiler an inlet 6 for cold air is arranged, to which a fan 60 is mounted for forced feeding of cold air to a convection space 7. A partition wall 70 is provided inside the convection space 7, which wall has a first, essentially horizontal, plane portion 70A and a second plane portion 70B which is angled downwards, which forms an angle β in relation to the horizontal plane. The partition wall 70 extends across the tube kit 4, which forces the air flow a to cross the tube kit 4 above the partition wall 70. The outlet 71 from the convection space 7 is arranged in connection to the left wall 9 a of the boiler housing 9. Thanks to the location of the opening 71 to the left in the figure, the air flow is thus forced after the first passage across the kit 4 to pass again across the tube kit 4 into channels 12 extending in connection to the upper part of the fire place 1, whereby the air flow a is forced to follow the passages from the left in the figure obliquely downwards to the right towards the outlet 8, which is located at the bottom at the opposite side in relation to the fire place 1.

At a typical operation case with a boiler according to the invention about 1000 m³ air/h is fed by means of the fan 60. When the air flow has been forced through the heat exchanger a temperature increase of about 60° C. is achieved. The output power obtained will then (depending on fuel/choice of burner) be between 15 and 25 kW with a boiler having a width b of about 0.5 m, a depth d of about 1 m and a height h of about 1.3 m. The fan 60 is suitably thermostatically controlled and starts at a stipulated temperature, normally 30 to 45° C., e.g. 38° C. The same thermostat is suitably used to switch off the burner at a maximally allowed temperature, normally 85 to 95° C., e.g. 90° C. According to the example, the fire place 1 contains about 70 litres and has twelve parallel tubes 40 as convectors.

In FIGS. 5 and 6 alternative embodiments of the tube kit 4 according to the invention are shown in the form of a cross-section perpendicular to its longitudinal extension. In FIG. 5 it is shown, like in FIG. 4, that circular-cylindrical tubes 40 are used, but with the difference that an even amount of tubes 40 is used in the respective row, namely three tubes 40 in each row and totally four rows implying a total of twelve tubes. Exactly as in the case of FIG. 4 the rows are displaced so that the tubes in the row just behind, seen in the flow direction a, are straight in front of the gap opening S of a row being ahead.

In FIGS. 6 a and 6 b the same kind of arrangement of the tube kit as in FIG. 5 is shown but with the difference that square tubes are used which are suitably positioned so that the front and back, respectively, corner (seen in the flow direction a) of each tube form a line which is essentially parallel with the main flow direction a.

In FIG. 7 an additional alternative embodiment according to the invention is shown. The embodiment shows that in certain cases the heat transmission ability may advantageously be increased with the respective tube 40 by longitudinally arranging an additional convection surface (more exactly two ones) centrally inside the tube 40 by longitudinally dividing the tube and then weld it together with a flat bar 42. The width x of the flat bar is then preferably larger than the diameter D of the tube 40, so that the longitudinal edges 42A, 42B protrude outside the surface of the tube on each side of the tube 40.

The invention is not limited to the above description but may be varied within the scope of the appending claims. The man skilled in the art for instance realizes that within the scope of the invention a great variation of different types of locations of the tubes 40 of the tube kit 4 is possible, wherein the above description thus only constitutes some examples. Thus, it is realized that many different types of combinations of the different numbers of tubes in rows and/or different numbers of rows and/or different sizes of tubes in different rows may be used in order to optimize different types of operation situations, for instance. Further, it is realized that the exact location of the different parts of a boiler according to the invention may be varied within rather wide frames but with maintained utilization of the main principles of the invention. In addition, it is obvious that the principles of a tube kit 4 according to the invention, especially with a convection space 7 according to the principles of the invention, may advantageously med used also in connection with other types of boilers, which are thus based on other general flow principles and it is therefore realized that the principles of the design of the tube kit, especially in connection with the principles of the convection space, may be the subject of an own, divisional patent application. 

1. A solid fuel boiler, comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage, and a boiler outlet for hot air, wherein the flue gas passage comprises a tube kit with a plurality of tubes arranged adjacent to each other to create a flow space for air between the tubes, wherein that at least one of said tubes is arranged so that it extends obliquely upwards in an angle a in relation to the vertical line L of the boiler from a lower attachment point to an upper attachment point.
 2. A solid fuel boiler according to claim 1, wherein that at least the main part of the tubes, preferably all tubes, are arranged so that they extend obliquely upwards, wherein the inlet and the outlet, respectively, of one tube are positioned along a line forming an acute angle in relation to the vertical line.
 3. A solid fuel boiler according to claim 2, wherein that said tubes are parallelly arranged and preferably are essentially straight tubes.
 4. A solid fuel boiler according to claim 2, wherein that said tubes are arranged in several rows in a displaced manner, whereby the hot air as to its main flow direction is forced to turn to and fro through the tube kit.
 5. A solid fuel boiler according to claim 1, wherein that the fire place is arranged at the bottom with its centre displaced towards a first side wall of the boiler, and that the flue gas outlet is arranged at the top, close to, or inside, a, in relation to said first side wall, opposite, second side wall of the boiler.
 6. A solid fuel boiler according to claim 1, wherein that the convection space is provided with at least one partition wall which is arranged to force the air flow essentially across the tube kit.
 7. A solid fuel boiler according to claim 6, wherein that said partition wall is arranged in such a manner that the air flow is forced to cross the tube kit at least twice.
 8. A solid fuel boiler according to claim 1, wherein that the air flow before its exit through the boiler outlet passes at least one passage having at least one wall, the opposite side of which is a delimitation of the fire place.
 9. A solid fuel boiler according to claim 1, wherein that the boiler outlet for hot air is arranged in the lower half of the boiler in level with said fire place.
 10. A solid fuel boiler according to claim 1, wherein that the boiler is provided with an essentially parallel-epipedic housing, wherein the height essentially exceeds the width and the depth, preferably h>d>b.
 11. A solid fuel boiler, comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage, and an boiler outlet for hot air, wherein the flue gas passage comprises a tube kit with a plurality of tubes arranged adjacent to each other to create a flow space for air between the tubes, wherein at least one of said tubes is arranged so that it extends obliquely upwards in an angle in relation to the vertical line L of the boiler from a lower attachment point to an upper attachment point, and wherein said convection space is provided with at least one partition wall which is arranged to force the air flow essentially across the tube kit in such a manner that the air flow is forced to cross the tube kit at least twice.
 12. A solid fuel boiler according to claim 11, wherein the boiler outlet for hot air is arranged in the lower half of the boiler in level with said fire place.
 13. A solid fuel boiler, comprising a fire place with a burner, a flue gas passage with a flue gas outlet, an inlet for cold air, a convection space for heat exchange of cold air with the flue gas passage, and an boiler outlet for hot air, wherein the flue gas passage comprises a tube kit with a plurality of tubes arranged adjacent to each other to create a flow space for air between the tubes, wherein at least one of said tubes is arranged so that it extends obliquely upwards in an angle in relation to the vertical line L of the boiler from a lower attachment point to an upper attachment point, and wherein said convection space is provided with at least one partition wall which is arranged to force the air flow essentially across the tube kit in such a manner that the air flow is forced to cross the tube kit at least twice, the boiler outlet for hot air is arranged in the lower half of the boiler in level with said fire place and the channels that connect the outlet opening of convection space with the boiler outlet, extend obliquely downwards, whereby the hot air flow is forced across the upper part of the fire place prior to exit via said boiler outlet. 